This invention relates to an apparatus for removing coke-like materials deposited on a top of a reactor for thermal cracking or catalytic cracking of heavy hydrocarbon oil in a fluidized bed or on a pipe inside surface of a transfer line from the reactor to scrubber.
As one of reactors for cracking reaction, wherein heavy hydrocarbon oil such as vacuum residual oil obtained as residues may vacuum distillation of petroleum, etc. is converted to light hydrocarbon oil or gasified, a fluidized bed type reactor using particles of heat carrier or particles of catalyst (such particles will be hereinafter referred to as fluidization particles) is utilized. In a reactor, fluidization particles are filled and formed into a fluidized bed by a fluidizing gas injected into the reactor at the lower part, while keeping the fluidized bed at a predetermined temperature. Then, heavy hydrocarbon oil is supplied by atomizing to the fluidized bed thus established, and converted to a gas, light hydrocarbon oil and coke by cracking.
The resulting product gas and light hydrocarbon product oil in a vapor state leave the fluidized bed as an effluent, including the fluidizing gas, and are led from the upper space part of the reactor through a transfer line to a successive refining system including a scrubber, a distillation column, etc.
Coke deposited on the fluidization particles is led to a regenerator together with the fluidization particles and removed from the fluidization particles by such a means as combustion, etc. The fluidization particles regenerated in the regenerator are heated to a predetermined temperature, and returned to the reactor.
The product gas and light hydrocarbon product oil in a vapor state produced by the cracking of heavy hydrocarbon oil move to a scrubber through a transfer line, where a portion of high boiling point materials in light hydrocarbon product oil vapors is condensed, and deposited as coke-like material. The deposition of coke-like materials in the transfer line increases a pressure drop in the transfer line and finally clogs the transfer line. Thus, it is an important problem to prevent the deposition of coke-like materials or remove the deposited coke-like materials.
The following apparatus are known for preventing the formation of the coke-like materials.
(1) Pipe inside surface of the transfer line is made from a plurality of tapered short pipes connected one to another with sharp recesses at the connections, showing a saw-toothed form with slow rise edge parts and sharp fall edge parts alternately in a running direction of the effluent gas when viewed in the longitudinal cross-sectional direction of the transfer line, and an inert gas is made to inject into the transfer line at each of the sharp fall parts in the running direction of the product gas to reduce a chance of contacting the effluent gas with the pipe inside surface (Japanese Patent Publication No. 23406/73).
(2) An alkali metal salt is applied to the pipe inside surface of the transfer line (Japanese Laid-open Patent Specification No. 134601/74).
(3) Temperature of the pipe wall of the transfer line is made (by about 100.degree. C.) higher than the effluent gas temperature (U.S. Pat. No. 2,881,130).
(4) a portion of coke as fluidization particles is blown through to scour out the coke-like materials deposited on the pipe inside surface of the transfer line (U.S. Pat. No. 2,735,806).
Apparatus (1) and (2) can reduce an amount of deposited coke-like materials, but cannot prevent the deposition thereof completely.
Heating apparatus (3)is effective, but cannot completely suppress the deposition of coke-like materials, and sometimes may increase the deposition, depending upon the temperature, to the contrary.
Apparatus (4) for blowing through the coke particles is simple and can scour out the deposited coke-like materials, and thus is practical in this respect. However, a large amount of the coke particles must be blown through. Specifically, more than 400 pounds of coke particles must be blown through per one barrel of a charge stock, and when such a large amount of the coke particles is recovered in a scrubber, etc. to return to the reactor together with the charge stock, a charge stock containing at least 50% by weight of the coke particles must be transferred, and many troubles are liable to occur in the scrubber and piping as cloggings by the coke particles or in pump operation, etc.